The present invention relates to a system for pumping fluid from multiple storage tanks and, in particular, it concerns a system for sequentially pumping fluid from multiple storage tanks using a single pump.
Various systems for pumping liquids from multiple sources to a single end point are known in the art. These include the use of separate pumps for each source, and a single pump coupled with separate on-off valves, or flow restrictors, associated with each source. Systems utilizing separate pumps suffer from extra cost and weight, along with the complexity of monitoring and actuating each pump when appropriate, especially if trying to synchronize the pumping rate so as to empty each of the tanks at substantially the same time. The issues of weight, monitoring and actuating is also true for systems using on-off valves to control the source of liquid flowing to the pump. Although flow restrictors do not allow for sequential emptying of a plurality of storage tanks, they provide a way to drain tanks of different volumes at different rates such that all of the tanks become empty at substantially the same time. When used with some liquids, such as aircraft fuel, these systems may create enough of a pressure drop after the flow restrictor to cause the fuel to vaporize in the fuel line before reaching the pump. Some of these systems are used in aircraft with the intention of pumping fuel from multiple fuel tanks located throughout the aircraft while maintaining the equilibrium of the aircraft.
It is known to provide gear pumps with multiple supply ports which supply liquid to the pump gears. The auxiliary supply ports of U.S. Pat. No. 3,083,819 to Mayes are configured as back-up or supplementary supply ports in case no, or insufficient, fuel is supplied to the pressurized primary supply port by a secondary pump located up stream from the main pump. All of the supply ports of Mayes receive fuel from a single tank. The injection port of Miles, U.S. Pat. No. 4,093,407, is configured to supply a limited quantity of a first liquid that will be mixed with a second liquid introduced at the primary supply port. During operation of the Miles pump the flow rate of the injected liquid is independent of the liquid flow rate caused by the gears of the pump. This requires additional flow control dedicated to the injection process. The liquids supplied to both ports are under pressure and both ports introduce liquids to the pumping gears during operation of the pump. U.S. Pat. No. 2,301,496, to Aldrich, discloses a gear pump in which liquid is introduced to the gear pump via a first supply port that is connected to a pressure release valve, such that liquid pumped out of the pump is reintroduced at the first supply port. Voids in the pumping volume of one of the gears, after the gear has passed the first supply port, are filled by liquid from the tank introduced by a second supply port that is connected to fuel tank. Therefore, the Aldrich system is essentially a circulation pump with a refill port that replaces any liquid lost from the system. The gear pump of U.S. Pat. No. 3,420,180, to Behrends et al., receives fluid from two sources, and includes a ratio-change passageway that provides a desired ratio of flow from the two sources. This arrangement is fine for a pump with only two supply ports connected to two different sources, it would, however, be inoperable in systems sequentially pumping from multiple tanks at different rates. The ratio-change passageway is also a problem for use with volatile liquids such as fuel where the pressure drop created in the passageway may cause the liquid to cavitate
The gear pumps of prior art cited above include multiple supply ports all of which are configured to supply fluid to the gears of a gear pump at all times during the operation of the pump with no consideration for sequential pumping from multiple sources. It should be noted that none of the above referenced prior art addresses a configuration whereby liquid is pumped from two or more tanks at different predefined flow rates by a single pump in such a way that there is no restriction likely to give rise to cavitation of the liquid being pumped.
There is therefore a need for a system for sequentially and/or parallel pumping of fluid from multiple storage tanks, without causing cavitation of the liquid, utilizing a single pump having multiple supply ports. It would be beneficial if the system also provide for pumping from different tanks at different predefined flow rates. It would be of further benefit if the system were configured so as to maintain the equilibrium of the platform on which the storage tanks are deployed.